A/D Converter of the CPCAI

[HAL6128]

There's a A/D Converter in the german CPCAI magazine from 08/1992:
http://www.cpcwiki.eu/imgs/9/9c/PCAI-92-08-044.jpg
http://www.cpcwiki.eu/imgs/b/b7/PCAI-92-08-045.jpg

On the mags first side there's a bill of material where a nf-transducer/transformer is listed but not which conversion ratio (1:1, 1:2 etc...). Has somebody a clue from looking at the schematic on the second page what kind of low-frequenz-transducer/transformer could it be?

Apart from this hardware topic: Which hardware extension is available or best for a real CPC to convert signals from analog to digital in case of sound sampling?

@Devilmarkus: I followed the thread http://www.cpcwiki.eu/forum/index.php?topic=2060.0 ("Digitizing music") and listend to your snapshot "okay". Impressive quality and a very long sound (about 5 minutes?). How did you do that?

[Bryce]

They actually do mention it in the parts list. I think they are refering to it with "Lautsprecherübertrager". ie: it should be one of the simple filters used in most speaker boxes. I would suggest a simple 1:1 coil. The nice thing about this circuit is that all parts including the ADC they've used are still readily available today.

Were there any commercial A/D converters for the CPC? I considered making one at one time, but I never got around to it, but it's still on my list of things to design/make.

Bryce.

[HAL6128]

Ok, thank you for your information.

The device is actually interesting in combination with the digiblaster. The sample source codes on page 3 (http://www.cpcwiki.eu/imgs/b/b8/PCAI-92-08-046.jpg) are small and - for my very basic assembler knowledge - understandable and therefore for me reproducible. Let's see.

[Bryce]

I just took another quick  look at the circuit. It's very strange. Why didn't they take the 5V supply from the expanion port that it's connected to? Where's the address decoding? What address does the software actually read?

Bryce.

[MaV]

Where's the address decoding? What address does the software actually read?

Hm, the last sentence on the second page is cut off. It seems that we're missing the pages with the software listings.

@hal 6128: Could you please scan the following pages so that we can answer the questions bryce has?

Of course, magazines are prone to error, which they normally correct a few issues later. hal should have a look at the issues after this for clarifications.

[TFM]

I just took another quick  look at the circuit. It's very strange. Why didn't they take the 5V supply from the expanion port that it's connected to? Where's the address decoding? What address does the software actually read?

Bryce.

Well, I remember... I built this device very accurate, and it did never work!

However, today I use the CPC Booster+ to sample, this one does work!

[TFM]

Hm, the last sentence on the second page is cut off. It seems that we're missing the pages with the software listings.

@hal 6128: Could you please scan the following pages so that we can answer the questions bryce has?

Of course, magazines are prone to error, which they normally correct a few issues later. hal should have a look at the issues after this for clarifications.

Like I remember this was one of the last issues of the CPC-AI. However all the scanned pages are in the Wiki:

http://mags.cpcwiki.eu/index.php?dir=1992

[MaV]

Like I remember this was one of the last issues of the CPC-AI. However all the scanned pages are in the Wiki:

http://mags.cpcwiki.eu/index.php?dir=1992

Ok, Thx. I'll have a look.

[HAL6128]

The A/D-Converter is also here in the Wiki in the DIY & Project Gallery:
http://www.cpcwiki.eu/index.php/PCAI_A/D_Converter_(DIY)

@TFM: It's a pitty that the CPCAI device doesn't work. Then it has no use.
A quick question: The CPC-Booster has two analog to digital converter (and also two DA converter), also 8-Bit resolution. Is it a advantage to use this for a stereo effect? What are your experiences with it? How long is it possible to record music or a sample?

[TFM]

Yes, you can use it for stereo.

The time you can use depends on quality and connected RAM. Or you can stream it from to hard-disc ;-)
Don't know exact values...

[Badstarr]

If the device doesn't work this may be completely academic but the reason why they might have used an external power source could be down to noise. Computers are noisy machines and sourcing power from it will cause the sampler to have all kinds of hum and buzz from CRT, disk access and RAM access introduced into it's signal. You can hear this if you plug your ipod into a powered dock and listen with headphones you will here all kinds of noise in silent parts of a track, but disconnect from the dock and it switches to an isolated power source (the battery) and the noise vanishes.


However, this could have been minimised via the use of a capacitor, so I could be wrong. 

[Bryce]

I thought at first that the ADC used might need an isolated supply, but I checked the datasheet and it doesn't. Noise is always a problem with an 8-Bit circuit, but as you said, this could easily be solved with good circuit design and a few cheap capacitors. A seperate supply is over the top.

I have an ADC 0804 here, when I have time I might build the circuit, improve it a little (lot) and let you know how it works.

Bryce.

[TFM]

I thought at first that the ADC used might need an isolated supply, but I checked the datasheet and it doesn't. Noise is always a problem with an 8-Bit circuit, but as you said, this could easily be solved with good circuit design and a few cheap capacitors. A seperate supply is over the top.

I have an ADC 0804 here, when I have time I might build the circuit, improve it a little (lot) and let you know how it works.

Bryce.

Well, I would be already glad if it would work at all.